1. Technical Field
The present invention contemplates the use of compositions to inhibit fibrinogen binding to endothelial cells for the purpose of inhibiting endothelial cell and fibrinogen mediated inflammation.
2. Background
Adhesion of leukocytes to vascular endothelium is one of the earliest events in a variety of immune-inflammatory reactions. The process participates in vascular occlusions and contributes to atherothrombotic lesions. At the molecular level, leukocyte adhesion to endothelial cells is a redundant mechanism, supported by the regulated recognition of a disparate set of membrane receptors, including integrins, expressed on both leukocytes and resting or cytokine-activated endothelial cells.
Integrins are a functionally and structurally related group of receptors that interact with a wide variety of ligands including extracellular matrix glycoproteins, complement and other cells. Integrins participate in cell-matrix and cell-cell adhesion in many physiologically important processes including embryological development, hemostasis, thrombosis, wound healing immune and nonimmune defense mechanisms and oncogenic transformation. See Hynes, Cell, 48:549-554 (1987). The majority of integrins participating in dynamic cell adhesion, bind a tripeptide, arginine-glycine-aspartic acid (RGD), present in their ligand, causing cell adhesion. See Ruoslahti et al., Science, 238:491-497 (1987).
Mac-1 (CD11b/CD18) is an integrin receptor found predominantly on macrophages and granulocytes. Like all integrin receptors, Mac-1 is a heterodimeric, transmembrane glycoprotein composed of non-covalently associated alpha and beta subunits.
Mac-1 mediates neutrophil/monocyte adhesion to vascular endothelium and phagocytosis of complement-opsonized particles. Antibodies to the Mac-1 receptor alter neutrophil function in vivo including inhibiting neutrophil migration into inflammatory sites. See Price et al., J. Immunol., 139:4174-4177 (1987). Mac-1 also functions as a receptor for fibrinogen in a reaction linked to fibrin deposition on the monocyte surface. See Altieri et al., J. Cell Biol., 107:1893-1900 (1988); Wright et al., Proc. Natl. Acad. Sci. USA, 85:7734-7738 (1938); Trezzini et al., Biochem. Biophys. Res. Commun., 156:477-484 (1988) and Gustafson et al., J. Cell Biol., 109:377-387 (1989).
Fibrinogen is a complex molecule of approximately 340,000 daltons and consists of three pairs of subunit polypeptides, called the xcex1, xcex2 and xcex3 chains. These individual chains are held together by several disulfide bonds. The proteolytic digestion of fibrinogen by plasmin produces fragments A, B, C, D and E, all having a molecular weight of less the 85,000 daltons. See Pizzo et al., J. Biol. Chem., 247:636-645 (1972).
Further proteolytic digestion of fibrinogen by plasmin produces a D30 fragment with a molecular weight of about 30,000 daltons containing portions of the xcex1, xcex2 and xcex3 chains of fibrinogen. See Furlan et al., Biochiem. Biophys. Acta., 400:95-111 (1975).
The deposition of fibrinogen on the leukocyte surface occurs in a variety of inflammatory responses such as delayed type hypersensitivity, incompatible transplant rejection and the physiopathology of vascular obstruction and atherogenesis. See Geczy et al., J. Immunol., 130:2743-2749 (1983); Hooper et al., J. Immunol., 126:1052-1058 (1981); Colvin et al., J. Immunol., 114:377-387 (1975); Hattler et al., Cell Immunology, 9:289-295 (1973); Gerrity, R. G., Am. J. Pathol., 103:181-190 (1981) and Am. J. Pathol., 103:191-200 (1981); and Shelley et al., Nature, 270:343-344 (1977).
Interactions of fibrinogen on cell surface receptors of endothelial cells have been described. Languino et al., Blood, 73:734 (1989) describe the binding of fibrinogen to endothelial cells by an RGD-dependent mechanism. It is generally believed that the vitronectin receptor is the major endothelial receptor for fibrinogen. Cheresh et al, Proc. Natl. Acad. Sci. USA, 84:6471-6475 (1987). Other endothelial cell receptors reported to bind fibrinogen include cell surface bound transglutaminase, and an 130 kilodalton receptor that binds to fibrin peptides. Erban et al., J. Biol. Chem., 267:2451 (1992).
Also on the surface of endothelial cells is an intercellular adhesion molecule 1 (ICAM-1) that has been described by Springer, Nature, 346:425-433 (1990), and has been shown to bind the leukocyte integrin LFA-1.
Recently, the interaction of fibrinogen with the Mac-1 receptor of leukocytes has been shown to be a dynamic cell adhesion reaction involving the recognition of the tripeptide RGD within fibrinogen by the Mac-1 receptor similar to the interaction of fibrinogen with the integrin receptors on platelets and endothelial cells. See Altieri et al., J. Clinic Invest., 78:968-976 (1986); Pytela et al., Science, 231:1559-1562 (1986); Ruoslahti et al., Science, 238:491-497 (1987); Ruoslahti et al., Cell, 44:517-518 (1986); and International PCT Application No. PCT/US91/05096.
It has now been discovered that fibrinogen binds to both the Mac-1 receptor on leukocytes and to an endothelial cell receptor (ECR), thereby bridging between the leukocyte and the endothelial cell during the process of inflammation. Inflammation arising from this bridging event is referred to as endothelial cell/fibrinogen-mediated inflammation. The ECR is an RGD-independent, fibrinogen specific receptor.
The invention describes novel compositions defining the binding sites for the interaction between ECR and fibrinogen.
Thus, a composition is contemplated comprising a therapeutically effective amount of a substantially pure and pharmaceutically acceptable fibrinogen homolog capable of binding to ECR and inhibiting Fg binding to endothelial cells. In preferred embodiments, ECR is ICAM-1.
A preferred Fg homolog is a polypeptide Fg homolog having an amino acid residue sequence derived from fibrinogen. A preferred polypeptide has a total sequence of from about 17 to 100 amino acid residues in length that includes the fibrinogen xcex3 chain sequence from fibrinogen xcex3 chain residues 117-133, which xcex3 chain sequence is shown in SEQ ID NO 2, and the polypeptide is capable of binding to ICAM-1 and inhibiting fibrinogen binding to endothelial cells, variants thereof, and compositions containing a Fg polypeptide homolog.
Also contemplated is an antibody that immunoreacts with a Fg polypeptide homolog as described herein. The antibody also immunoreacts with fibrinogen and inhibits fibrinogen binding to endothelial cells.
Also contemplated is a composition comprising a therapeutically effective amount of a substantially pure and pharmaceutically acceptable ICAM-1 homolog capable of binding to fibrinogen and inhibiting fibrinogen binding to endothelial cells.
The invention also describes a monoclonal antibody that immunoreacts with ICAM-1, but does not immunoreact with the vitronectin receptor, such that the monoclonal antibody preferentially inhibits fibrinogen binding to stimulated endothelial cells.
A monoclonal antibody is also described that immunoreacts with fibrinogen and that preferentially inhibits fibrinogen binding to stimulated endothelial cells.
Also described is a method of inhibiting fibrinogen (Fg) binding to endothelial cells comprising contacting the endothelial cells with a Fg-binding inhibiting amount of a physiologically acceptable composition comprising a homolog selected from the group consisting of a Fg homolog and an ICAM-1 homolog.
The method is useful for inhibiting fibrinogen/endothelial cell-mediated inflammation in a patient and comprises administering to a patient a therapeutically effective amount of a pharmaceutically acceptable composition comprising a substantially pure homolog selected from the group consisting of a Fg homolog and an ICAM-1 homolog.
The invention also describes a method of detecting the amount of a fibrinogen (Fg) homolog in a liquid sample comprising:
(a) admixing a sample of stimulated endothelial cells with a predetermined amount of a liquid sample containing a Fg homolog and a predetermined amount of labelled Fg homolog to form a competition reaction admixture;
(b) maintaining the reaction admixture for a predetermined time period sufficient for any Fg homolog present in said composition to bind to the endothelial cells and form an endothelial cell:Fg homolog complex and to allow the labelled Fg homolog to bind to the endothelial cells to form a labelled endothelial cell:Fg homolog complex; and
(c) assaying for the amount of labelled endothelial cell:Fg homolog complex formed in step (b) thereby detecting the amount of a Fg homolog in the composition.
Also described is a method of screening for compositions effective at inhibiting fibrinogen binding to ICAM-1 comprising the steps of:
a) admixing in an inhibition reaction admixture preselected amounts of a putative inhibitor composition, a fibrinogen homolog, and an ICAM-1 homolog;
b) maintaining the admixture under conditions sufficient for the ICAM-1 homolog to bind to the Fg homolog and form an ICAM-1 homolog:Fg homolog complex; and
c) measuring the amount of ICAM-1 homolog:Fg homolog complex formed in step (b), and thereby the effectiveness of the inhibitor composition.
Also described is a method for preparing substantially pure ICAM-1 comprising the steps of:
(a) providing an aqueous detergent composition containing at least ICAM-1;
(b) contacting the ICAM-1-containing composition with a fibrinogen-immobilized matrix comprising fibrinogen affixed to a solid support, wherein the contacting is conducted under conditions sufficient for the ICAM-1 to bind to the fibrinogen and form a solid phase ICAM-1:fibrinogen complex;
(c) washing the solid support and the complex with an aqueous wash buffer comprising Mg++, Mn++ and an RGD-containing polypeptide under conditions sufficient to elute any proteins bound to fibrinogen in an RGD-dependent manner, wherein the wash buffer is substantially free from Ca++; and
(d) eluting the ICAM-1 from the solid support using an aqueous buffer comprising Mg++, Mn++ and EDTA, to form the substantially pure ICAM-1.